Exercise 2.1 - Answers

1

This
is. If j and y are replaced by declarative sentences, the
result will be a declarative sentence.

(ii)

This
isn't. Replacing j and y with declarative sentences will result in
ungrammatical nonsense; for instance:

John is a man and Mary is a woman will both be there.

(iii)

This
isn't. The result of replacing j by a declarative sentence will be a sentence,
but not a declarative sentence. ("Please make sure that
the door is shut" is not the sort of thing that can be true or
false.)

(iv)

This
is.

(v)

This isn't. The result
of replacing j by a declarative sentence will be a question.

(vi)

This
is. (It is, of course, similar to the previous example, and they could
often be used interchangeably. But that just shows that a declarative
sentence and a question can sometimes be used interchangeably.)

(vii)

Surely
this isn't. Consider, for example, "John stands up whenever
Mary sits down". This does not consist of "j
whenever y" together with the declarative sentences,
"John stands up" and "Mary sits down". (Think
of the various things that these sentences can mean if used on their
own, and ask yourself whether that is what they mean in the
original sentence.) Try some other examples. In fact "whenever"
plays the same sort of role as, for instance, "whoever"
in, "Whoever is knocking at the door is angry". And clearly
"whoever j, y" is not a sentence-functor. (We could paraphrase"John
stands up whenever Mary sits down" as "At whatever time
John stands up, Mary sits down".)

(viii)

It
isn't. Replacing j and y
with declarative sentences will not result in a single sentence.
However, it must be said that Descartes sometimes talks as if "I
think, therefore I am" expresses a single proposition. Nonetheless,
it is surely not correct to ask, "Is it true that I think, therefore
I am?" And this suggests that "I think, therefore I am"
is not a single declarative sentence.